The present invention relates broadly to improved scissors as used in horticulture and for industrial purposes, and more specifically to improved scissors having two blades, one of which is metallic while the other is ceramic.
Because ceramics have various excellent characteristics as compared with metals, and because of rapid progress made in recent years in the technique for working ceramics, it has been proposed to use ceramics instead of steel as a material for scissors as described in the Japanese laid-open utility model application No. 56-104450 and others.
The trouble is that ceramics are less tenacious than metals, although they have extra-high abrasion resistance. Low mechanical strength resulting therefrom causes the two blades of scissors to be liable to chip when both of them are made of ceramics. Once they have chipped, it is difficult to recondition them.
FIG. 3 illustrates a pair of scissors previously proposed by the present inventor in the form of the Japanese laid-open utility model application No. 59-90762 as an attempt to solve the above problem. The basic principle of this attempt resides in that the above-described disadvantage will be eliminated if one of the two blades of scissors is made of a ceramic which obviates the necessity of grinding and the other is made of a metal which can be easily ground. An important feature of the scissors shown in FIG. 3 is that the cutting edge of a metallic blade 1 has an acute included angle while the cutting edge of a ceramic blade 2 has an included angle larger than that of the metallic blade 1 and smaller than a right angle.
Normally, the flat sides of the blades 1 and 2 lie on a virtual plane AB (FIG. 3), and the beveled sides of these blades are disposed opposite to each other across the virtual plane AB. However, when the cutting edges cut into an article C, the article C splitting ahead of the cutting edges tends to react upon the cutting edges so as to allow them to trespass on the opposite sides of the virtual plane AB as shown with arrows in FIG. 3.
The blades 1 and 2 have a rivet or screw connection 3 (FIG. 4) between the cutting ends P and the handle ends. The two blades are made to twist or curve slightly toward one another so that they touch in only two places, i.e., at a point Q just behind the pivot 3 and at a point P' (FIG. 5) along the blades where the cutting is taking place. When the blades 1 and 2 are completely closed, they are in touch with each other only at the points P and Q, with a gap S (FIG. 4) left between the middle portions of the blades 1 and 2. Because of their elasticity, the blades 1 and 2 apply contact pressure to each other while they are being closed. As they are closed, the contact point P' shifts from right to left as viewed on FIG. 5. The blades 1 and 2 cross each other when the contact point P' is midway between the pivot 3 and the cutting ends P.
Thus the scissors shown in FIG. 3 also have the disadvantage that the ceramic blade 2 is liable to chip when a hard article C is cut in the middle portions of the blades 1 and 2, because the left-hand halves of the blades 1 and 2 as viewed on FIG. 5 interfere with each other as they are closed.